18. 4Sum

https://leetcode.com/problems/4sum/description/
输入: 数组 和 target
输出: 4个数字相加等于 target 的所有组合

和3sum 一样,多了个循环

class Solution {
    public List> fourSum(int[] nums, int target) {
        Arrays.sort(nums);
        List> res=new ArrayList>();
        for(int i=0;i0&&nums[i]==nums[i-1]){
                continue;
            }
            for(int j=i+1;ji+1&&nums[j]==nums[j-1]){
                    continue;
                }
                int k=j+1;
                int m=nums.length-1;
                while(k=0&&nums[m]==nums[--m]);
                        while(k+1target){
                        m--;
                    }else{
                        k++;
                    }
                }
            }
        }
        return res;
    }
}